Functional changes, following X-irradiation of the right visual cortex with 3,500 rads in a single exposure, are monitored by evoked electroencephalographic responses of the right and the left homologous, non-irradiated cortex, from photic stimulation of the retina. Cerebral spinal fluid pressure, in the spinal subarachnoid space, is monitored by a catheter-reservoir system. Funduscopic changes are recorded by an appropriate camera. Structural changes are determined at sequential intervals by examination with routine and special histological techniques. With the preceding, two phenomena are receiving especial attention: Delayed brain swelling and retrograde transsynaptic degeneration in the visual system. An additional series of monkeys are receiving whole brain irradiation with 6000 rads in divided doses over six weeks, a regimen that simulates therapeutic trials in humans. This series will be monitored as indicated above. Eighteen adult Macaca mulatta will be exposed to 6000 rads of super voltage irradiation to the whole brain over a period of six weeks. Functional changes will be monitored by funduscopic photography and CSF protein and lactic dehydrogenase content. The pathogenesis of delayed lesions will be determined by sequential sacrifice over a period of 52 weeks.